Amplifier with built in time gain compensation for ultrasound applications

ABSTRACT

An ultrasound circuit comprising a trans-impedance amplifier (TIA) with built-in time gain compensation functionality is described. The TIA is coupled to an ultrasonic transducer to amplify an electrical signal generated by the ultrasonic transducer in response to receiving an ultrasound signal. The TIA is, in some cases, followed by further analog and digital processing circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation claiming the benefit under 35 USC§120 of U.S. patent application Ser. No. 16/011,755, filed Jun. 19, 2018under Attorney Docket No. B1348.70048US01, and entitled “AMPLIFIER WITHBUILT IN TIME GAIN COMPENSATION FOR ULTRASOUND APPLICATIONS,” which ishereby incorporated herein by reference.

U.S. application Ser. No. 16/011,755 claims the benefit under 35 USC§119(e) of U.S. Provisional Patent Application Ser. No. 62/522,622,filed Jun. 20, 2017 under Attorney Docket No. B1348.70048US00, andentitled “AMPLIFIER WITH BUILT IN TIME GAIN COMPENSATION FOR ULTRASOUNDAPPLICATIONS,” which is hereby incorporated herein by reference.

BACKGROUND Field

The present application generally relates to ultrasound devices havingan amplifier for amplifying received ultrasound signals.

Related Art

Ultrasound probes include one or more ultrasound sensors which senseultrasound signals and produce corresponding electrical signals. Theelectrical signals are processed in the analog or digital domain.Sometimes, ultrasound images are generated from the processed electricalsignals.

BRIEF SUMMARY

According to an aspect of the present application, an ultrasoundapparatus is provided, comprising an ultrasound sensor and atrans-impedance amplifier (TIA) coupled to the ultrasound sensor andconfigured to receive and amplify an output signal from the ultrasoundsensor. The TIA may include time gain compensation (TGC) functionality,and thus the ultrasound device may lack a distinct TGC circuitdownstream in the analog signal processing chain. While a TIA is oneexample of a suitable amplifier, other types of amplifiers may be used,such as low noise amplifiers (LNAs) or trans-conductance amplifiers.

According to an aspect of the present application, an ultrasoundapparatus is provided, comprising an ultrasonic transducer to provide ananalog electrical signal, and an amplifier having time gain compensation(TGC) functionality coupled to the ultrasonic transducer and configuredto receive and amplify the analog electrical signal by a time-dependentamount.

According to an aspect of the present application, an ultrasound circuitis provided, comprising an ultrasound transducer, an analog signalprocessing chain coupled to the ultrasonic transducer, and ananalog-to-digital converter (ADC), wherein the analog signal processingchain is coupled electrically between the ultrasonic transducer and theADC, wherein the analog signal processing chain includes a combinedtrans-impedance amplifier (TIA) and time gain compensation (TGC)circuit.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments of the application will be describedwith reference to the following figures. It should be appreciated thatthe figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same reference number in all thefigures in which they appear.

FIG. 1 is a block diagram of an ultrasound device including an amplifierfor amplifying an ultrasound signal, according to a non-limitingembodiment of the present application.

FIG. 2 illustrates an ultrasound signal receive circuitry chainincluding a trans-impedance amplifier (TIA) with time gain compensation(TGC) functionality and a plurality of analog signal processing stagesfollowing the TIA, according to a non-limiting embodiment of the presentapplication.

FIG. 3 is a block diagram of a TIA with TGC functionality, according toa non-limiting embodiment of the present application.

FIG. 4A is a circuit diagram of an implementation of a TIA with TGCfunctionality, according to a non-limiting embodiment of the presentapplication.

FIG. 4B is a circuit diagram of an implementation of a TGC controlsignal switching circuit, according to a non-limiting embodiment of thepresent application.

FIG. 4C is a circuit diagram of an implementation of a TGC controlsignal switching circuit, according to a non-limiting embodiment of thepresent application.

FIG. 4D illustrates an exemplary operating sequence for TGC controlsignals, according to a non-limiting embodiment of the presentapplication.

DETAILED DESCRIPTION

Aspects of the disclosure relate to amplification circuitry for anultrasound device. An ultrasound device may include one or moreultrasonic transducers configured to receive ultrasound signals andproduce electrical output signals. Thus, the ultrasonic transducers maybe operated as ultrasound sensors. The ultrasound device may include oneor more amplifiers for amplifying the electrical output signals. In someembodiments, the amplifier(s) may be a trans-impedance amplifier (TIA)and may include time gain compensation (TGC) functionality. Analogprocessing stages (alternatively referred to herein as “blocks” or“components”) may follow the TIA to perform various analog processingfunctions, such as averaging electrical signals produced by multipleTIAs of the ultrasound device. In at least some embodiments, theultrasound device lacks a distinct TGC stage or circuit downstream ofthe TIA. While a TIA represents one example of a suitable amplifiertype, other types of amplifiers may alternatively be employed, includingLNAs or trans-conductance amplifiers.

According to an aspect of the present application, a method ofprocessing ultrasound signals is provided. The method comprisesgenerating an electrical signal using an ultrasonic transducer followedby amplifying and time gain compensating the electrical signal with aTIA, LNA, trans-conductance amplifier, or other suitable amplifier. Forsimplicity of discussion, a TIA is explicitly described here. In someembodiments, multiple TIAs are provided, and further processingcomprises averaging the signals provided by multiple TIAs. The averagedsignal may then be digitized by a suitable analog-to-digital converter(ADC). In some implementations, multiple TIAs (or other amplifiers) areprovided, and further processing comprises using cross-coupled switchesto flip the polarity of some signals to enable coded reception, such asthe use of Hadamard coding.

The aspects and embodiments described above, as well as additionalaspects and embodiments, are described further below. These aspectsand/or embodiments may be used individually, all together, or in anycombination of two or more, as the application is not limited in thisrespect.

FIG. 1 illustrates a circuit for processing received ultrasound signals,according to a non-limiting embodiment of the present application. Thecircuit 100 includes N ultrasonic transducers 102 a . . . 102 n, whereinN is an integer. The ultrasonic transducers are sensors in someembodiments, producing electrical signals representing receivedultrasound signals. The ultrasonic transducers may also transmitultrasound signals in some embodiments. The ultrasonic transducers maybe capacitive micromachined ultrasonic transducers (CMUTs) in someembodiments. The ultrasonic transducers may be piezoelectricmicromachined ultrasonic transducers (PMUTs) in some embodiments.Alternative types of ultrasonic transducers may be used in otherembodiments.

The circuit 100 further comprises N circuitry channels 104 a . . . 104n. The circuitry channels may correspond to a respective ultrasonictransducer 102 a . . . 102 n. For example, there may be eight ultrasonictransducers 102 a . . . 102 n and eight corresponding circuitry channels104 a . . . 104 n. In some embodiments, the number of ultrasonictransducers 102 a . . . 102 n may be greater than the number ofcircuitry channels.

The circuitry channels 104 a . . . 104 n may include transmit circuitry,receive circuitry, or both. The transmit circuitry may include transmitdecoders 106 a . . . 106 n coupled to respective pulsers 108 a . . . 108n. The pulsers 108 a . . . 108 n may control the respective ultrasonictransducers 102 a . . . 102 n to emit ultrasound signals.

The receive circuitry of the circuitry channels 104 a . . . 104 n mayreceive the (analog) electrical signals output from respectiveultrasonic transducers 102 a . . . 102 n. In the illustrated example,each circuitry channel 104 a . . . 104 n includes a respective receivecircuit 110 a . . . 110 n and an amplifier 112 a . . . 112 n. Thereceive circuit 110 a . . . 110 n may be controlled toactivate/deactivate readout of an electrical signal from a givenultrasonic transducer 102 a . . . 102 n. An example of suitable receivecircuits 110 a . . . 110 n are switches. That is, in one embodiment thereceive circuits are controllable switches which are switched duringtransmit mode to disconnect the ultrasonic transducers from the receivecircuitry and during receive mode to connect the ultrasonic transducersto the receive circuitry. Alternatives to a switch may be employed toperform the same function.

The amplifiers 112 a . . . 112 n may be TIAs with built-in TGCfunctionality in some embodiments, outputting amplified and time gaincompensated analog signals. The use of TIAs with built-in TGCfunctionality may facilitate low power operation of the circuit 100compared to use of alternative amplifier designs. Also, the use of a TIAwith built-in TGC functionality may allow for omission of any downstreamTGC stages or circuits, which may further aid in power reduction.

The circuit 100 further comprises an averaging circuit 114, which isalso referred to herein as a summer or a summing amplifier. In someembodiments, the averaging circuit 114 is a buffer or an amplifier. Theaveraging circuit 114 may receive output signals from one or more of theamplifiers 112 a . . . 112 n and may provide an averaged output signal.The averaged output signal may be formed in part by adding orsubtracting the signals from the various amplifiers 112 a . . . 112 n.The averaging circuit 114 may include a variable feedback resistance.The value of the variable feedback resistance may be adjusteddynamically based upon the number of amplifiers 112 a . . . 112 n fromwhich the averaging circuit receives signals. In some embodiments, thevariable resistance may include N resistance settings. That is, thevariable resistance may have a number of resistance settingscorresponding to the number of circuitry channels 104 a . . . 104 n.Thus, the average output signal may also be formed in part byapplication of the selected resistance to the combined signal receivedat the inputs of the averaging circuit 114.

In some embodiments, the averaging circuit 114 also includes built-inTGC functionality. Such functionality may expand on the TGC functionperformed by the amplifiers 112, and thus may further facilitateomission of a distinct downstream TGC circuit. Any suitable TGCcircuitry may be included in the averaging circuit 114.

The averaging circuit 114 is coupled to an ADC 126 via ADC drivers 124.As should be appreciated from FIG. 1, in some embodiments the outputterminal of the averaging circuit is directly coupled to the ADCdrivers, without intervening processing stages. In the illustratedexample, the ADC drivers 124 include a first ADC driver 125 a and asecond ADC driver 125 b. The ADC 126 digitizes the signal(s) from theaveraging circuit 114.

While FIG. 1 illustrates a number of components as part of a circuit ofan ultrasound device, it should be appreciated that the various aspectsdescribed herein are not limited to the exact components orconfiguration of components illustrated. For example, aspects of thepresent application relate to the amplifiers 112 a . . . 112 n, and thecomponents illustrated downstream of those amplifiers in circuit 100 areoptional in some embodiments.

The components of FIG. 1 may be located on a single substrate or ondifferent substrates. For example, as illustrated, the ultrasonictransducers 102 a . . . 102 n may be on a first substrate 128 a and theremaining illustrated components may be on a second substrate 128 b. Thefirst and/or second substrates may be semiconductor substrates, such assilicon substrates. In an alternative embodiment, the components of FIG.1 may be on a single substrate. For example, the ultrasonic transducers102 a . . . 102 n and the illustrated circuitry may be monolithicallyintegrated on the same die (e.g., a semiconductor die, such as silicon).Such integration may be facilitated by using CMUTs as the ultrasonictransducers.

According to an embodiment, the components of FIG. 1 form part of anultrasound probe. The ultrasound probe may be handheld. In someembodiments, the components of FIG. 1 form part of an ultrasound patchconfigured to be worn by a patient or part of an ultrasound pill to beswallowed by a patient.

FIG. 2 illustrates an ultrasound signal receive circuitry chainincluding a TIA with time gain compensation (TGC) functionality and aplurality of analog signal processing stages following the TIA,according to a non-limiting embodiment of the present application. FIG.2 includes amplifier 112 a, averaging circuit 114, ADC driver 124, andADC 126, the latter two of which are illustrated as a single block forease of explanation.

In some implementations, the amplifier 112 a is a TIA with built-in TGCfunctionality, outputting amplified and time gain compensated analogsignals. Integrating TGC functionality into amplifier 112 a mayfacilitate low power operation of the circuit 100 compared to use ofalternative amplifier designs. The use of an amplifier 112 a withbuilt-in TGC functionality may allow for omission of any downstream TGCstages or circuits, as is the case in FIG. 2, which may further aid inpower reduction and design simplification. The amplifier 112 a receivesan electrical signal representing an ultrasound signal received by theultrasound transducer. The amplifier 112 a applies at least a minimalgain to the electrical signal as part of TIA functionality.Additionally, amplifier 112 a will provide an additional, time dependentamount of gain representing TGC functionality to compensate forattenuation of signals.

The gain provided by the illustrated TIA with TGC functionality mayassume any suitable values. For example, the gain from the TIAfunctionality may be on the order of 90 decibels (e.g., between 50 and100 dB) and the gain from TGC functionality may be a fraction of that(e.g., from zero to 18 dB, or any other suitable value). Thus, as anon-limiting example, the total gain provided by the illustrated TIAwith TGC functionality may range significantly depending on the point intime of reception of the ultrasound signal. As one example, the gain mayrange between 90 and 108 dB during reception of a signal.

While FIG. 2 illustrates TIA 112 a, it should be appreciated that any ofthe TIAs 112 a . . . 112 n may have the configuration shown in FIG. 2.

The averaging circuit 114 receives the output of the amplifiers 112 a .. . 112 n. In some embodiments, the averaging circuit may improve theultrasound signal to noise ratio and/or may provide TGC functionality.As a non-limiting example, the averaging circuit provides between 5 dBand 20 dB (e.g., a 9 dB) improvement to the signal to noise ratio and upto an additional 10-20 dB (e.g., 11 dB) of TGC. The averaging circuit114 is coupled to an ADC 126 via ADC drivers 124. As should beappreciated from FIG. 1, in some embodiments the output terminal of theaveraging circuit is directly coupled to the ADC drivers, withoutintervening processing stages. The ADC 126 digitizes the signal(s) fromthe averaging circuit 114.

FIG. 3 is a block diagram of a TIA with TGC functionality (e.g. one ofthe amplifiers 112 a . . . 112 n), according to a non-limitingembodiment of the present application. FIG. 3 includes input terminal330, amplifier 332, output terminal 336, and variable impedance feedbackcircuit 334. The input terminal 330 receives analog electrical signalsrepresenting ultrasound signals. In some implementations, the inputterminal 330 is in electrical communication with an ultrasoundtransducer, e.g. any one of the transducers 102 a . . . 102 n, eitherthrough a direct coupling or through a switch, e.g. any one of theswitches 110 a . . . 110 n.

The signals received at the input terminal 330 are amplified by theamplifier 332. The amount of gain may be selected to provide sufficientdynamic range for subsequent processing and digitization of the signaloutput at output terminal 336. In some implementations, the amplifierwill provide a gain between 90 dB and 120 dB, as a non-limiting example.In some implementations, the amount of gain is dynamically varied overtime to provide TGC that compensates for ultrasound signal attenuation.

The signal at output terminal 336 is fed back to the input terminal 330of the amplifier 332 through the variable impedance feedback circuit334, which is used to modify the gain of TIA 112. Variable impedancefeedback circuit 334 may be configured to generate—using timingcircuitry or otherwise—or alternatively to receive—from a digitalcontroller, processor, or other source—one or more control signals thatdynamically adjust the feedback impedance seen by amplifier 332 in orderto provide a time-varying amount of gain that can be used to provide TGCfunctionality. In some implementations, amplifier 332 may be anamplifier besides a TIA, such as a low noise amplifier (LNA) ortrans-conductance amplifier. In some implementations, amplifier 332 maybe a voltage amplifier and input terminal 330 may be connected to apiezoelectric transducer.

FIG. 4A illustrates a circuit schematic for a TIA with TGC functionality(e.g. one of the amplifiers 112), according to a non-limiting embodimentof the present application. FIG. 4A includes input terminal 330,amplifier 332, variable impedance feedback circuit 334, and outputterminal 336. Amplifier 332 includes an NMOS transistor 440, NMOStransistor 442, current source 444, PMOS transistor 446, and currentsource 448. Variable impedance feedback circuit 334 includes a number,N, of NMOS transistors 450 a . . . 450 n configured to receive Nrespective control signals CTRL[0] . . . CTRL[N], a number, N, ofresistors 452 a . . . 452 n, and a number, M, of capacitors 454 a . . .454 m.

An analog electrical signal from an ultrasound transducer is received atthe input terminal 330. The input is connected to the gate of the NMOStransistor 440, the source being connected to ground and the drain beingconnected to the NMOS transistor 442. The gate of the NMOS transistor442 is connected to a bias voltage that may be configured to change thegain of the amplifier. In some implementations, the NMOS transistor 442is omitted and NMOS transistor 440 is directly coupled to the currentsource 444. In some implementations, current source 444 may beimplemented using one or more transistors (e.g., one, two, or more PMOStransistors), not shown in FIG. 4A. Current source 444 may beimplemented using any suitable current source circuitry.

The gate of the NMOS transistor 446 is connected to the output of thecurrent source 444 and the drain of the NMOS transistor 442. The drainof NMOS transistor 446 is connected to a positive power supply voltage,and the source of NMOS transistor 446 is connected to current source448, the output 336, and the variable impedance feedback circuit 334.The current source 448 may be implemented as one or more transistors, aresistor, or any suitable circuitry.

The variable impedance feedback circuit 334 is coupled to the outputterminal 336 and the input terminal 330. The variable impedance feedbackcircuit 334 receives the N control signals, CTRL[0], CTRL[1] . . .CTRL[N], at the NMOS transistors 450 a . . . 450 n that are used toconfigure the impedance of the feedback path from the output 336 to theinput 330. When the control signal CTRL[0] is high, a logical one, theNMOS transistor 450 a completes a feedback path, from the outputterminal 336 to the input terminal 330, that includes resistor 452 a.When the control signal CTRL[0] is low, a logical zero, the NMOStransistor 452 a breaks the feedback path. If CTRL[1] is asserted highwhile CTRL[0] is low, the NMOS transistor 450 b completes a feedbackpath, from the output terminal 336 to the input terminal 330, thatincludes the resistor 452 b and the resistor 452 a, which has increasedimpedance relative to the feedback path with the resistor 452 a as thesole resistor. In this manner, the amplifier gain may be increased.

The resistors 452 a . . . 452 n may have any suitable relationship toprovide varying gain. For example, in some implementations, theresistors 452 a . . . 452 n provide resistance values that changesequentially from resistor 452 a to resistor 452 n. In someimplementations, the resistors 452 a . . . 452 n are sized so thatadding an additional resistor to the feedback path, e.g. by switchingoff a first transistor of the NMOS transistors 450 a . . . 450 n andswitching on a second one of the NMOS transistors 450 a . . . 450 n thatis adjacent to the first transistor and closer to the Nth transistor,creates a logarithmically scaled increase in the gain of the amplifier112. For example, the resistor 452 a may be sized to provide 90 dB ofgain and each resistor that is added to the feedback path maysubsequently, may increase the gain by one decibel. In someimplementations, the resistance of each resistor of the resistors 452 a. . . 452 n or a subset of the resistors 452 a . . . 452 n is scaled bya constant scaling factor, e.g., each resistor in a subset of theresistors 452 a . . . 452 n has 10%, 20%, 30%, or more resistance thanthe adjacent resistor more proximate to the input 330. In someimplementations, the resistance of one or more (e.g., each) resistors isscaled so that the characteristic RC time constant of the variableimpedance feedback circuit 334 is scaled by a constant factor with eachadditional resistor on the feedback path. Configuring the resistors inany of the manners describe may facilitate providing variable gain, andthus achieving TGC functionality.

The capacitor 454 a is shown connected in parallel with the resistors452 a and 452 b. In some implementations, there may be one capacitor foreach grouping of resistor, transistor, and control signal. For example,in some embodiments the number of capacitors M is equal to the number ofresistors N. In some implementations, each capacitor is in parallel withone or more resistors. For example, each capacitor may be in parallelwith two resistors and M may be one half of N. The capacitors 454 a . .. 454 m may be sized and arranged with one or more resistors each toaddress various designs concerns, such as area, cost, and bandwidth,without departing from the scope of the present application.

FIG. 4B illustrates a circuit schematic for a TGC control signalswitching circuit, charge pump circuit 460, according to a non-limitingembodiment of the present application. FIG. 4B includes switch signalinput 462, switch 464, current source 470, current source 472, capacitor474, and control signal output 476. To activate or deactive a givencontrol signal, e.g., one of CTRL[0] . . . CTRL[N] discussed withreference to FIG. 4A, a switching signal, SW0, is received at the switchsignal input 462. The switch 464 includes PMOS transistor 466 and NMOStransistor 468, which both have respective gates connected to receivethe switch signal input 462. The PMOS transistor 466 and the NMOStransistor 468 are shown in an inverter arrangement, such that thecontrol signal output 476 will be the logical opposite of switch signalinput 462. However, any suitable switching means may be used in theswitch 464.

The output of the switch 464 is connected to the capacitor 474, which isconfigured to slow the edges of control signal output 476 duringtransitions between logic levels. Since the ultrasound transducer isreceiving a continuous signal, abrupt changes in the control signal, andtherefore the gain of amplifier 112 a (or any of amplifiers 112 b . . .112 n), could create transient errors, such as a glitch, in theultrasound measurements. By slowing the transitions between logic levelfor the control signal output 476, capacitor 474 can prevent, reduce,and/or substantially eliminate transient switching errors from theultrasound measurements such that the impact to the ultrasoundmeasurement of altering the gain of amplifier 112 is dominated by thedesired increase in gain and switching errors are comparativelynegligible.

During transitions from low to high output, the capacitor charges andslows the rise time of the output. During transitions from high to lowoutput, the capacitor discharges over time to slow the transition. Amaximum transition time for the output may be specified to achieve asufficiently rapid rate of TGC control transitions, e.g. 0.005 dB per 10nanoseconds, 0.01 dB per 10 nanoseconds, 0.01 dB per nanosecond, 0.1 dBper nanosecond, or 0.2 dB per nanosecond or any other suitable value. Itshould be appreciated that the transition profile (gain/attenuationcurve) determined by the amplifier 112 and TGC ciruitry (e.g. 334 and460) should be present in the digital domain after digitization by theADC (e.g. 126). Due to the physics of the circuitry involved, thedigitized transition profile may differ from an ideal or targettransition profile, and the differences between the actual and targetprofiles may be corrected in the digital domain, for example, bymodeling the gain circuitry and applying a digital gain configured toeliminate the discrepancy. In some implementations, adjustments are madeto the digital signal based on a model of the gain circuitry, e.g. amodel of the transitions between levels of impedance feedback used toincrease the gain, and not based on any specific, desiredgain/attenuation curve.

Capacitor 474 may be any suitably sized capacitor. For example, thecapacitor may have a size of 100 femtofarads, 200 femtofarads, 500femtofarads, 1 picofarad, or any other suitable capacitance value. Insome implementations, capacitor 474 may be implemented using multiplecapacitors arranged in an array. In some implementations, the amount ofcapacitance may be dynamically switched using control signals orotherwise configurable or programmable, e.g. by using transistors toconnect each transistor in the array to the control signal output 476.The amount of capacitance connected between ground and control signaloutput 476 can be varied to control the slew rate of the amplifier andTGC, depending on the amount of glitch error energy that can betolerated in the measurements. For example, smaller capacitance valuesmay be selected from an array of capacitors when rapid TGC operation isrequired and relatively high levels of glitch energy can be tolerated.Alternatively, other circuitry may be implemented to store and releaseelectrical charge—in sufficient quantities and for sufficientdurations—to avoid having the control signal transitions introducetransient errors that would degrade the ultrasound readings.

FIG. 4C illustrates a circuit schematic for a TGC control signalswitching circuit, charge pump circuit 461 according to a non-limitingembodiment of the present application. FIG. 4C includes the samecomponents as the charge pump circuit of FIG. 4B but arrangeddifferently. Thus, charge pump circuit 461 includes switch signal input462, PMOS transistor 466, NMOS transistor 468, current source 470,current source 472, capacitor 474, and control signal output 476. Toactivate or deactive a given control signal, e.g., one of CTRL[0] . . .CTRL[N] discussed with reference to FIG. 4A, a switching signal, SW0, isreceived at the switch signal input 462. PMOS transistor 466 and NMOStransistor 468, which were discussed with reference to switch 464 inFIG. 4B, both have respective gates connected to receive the switchsignal input 462. The PMOS transistor 466 and the NMOS transistor 468are shown in an inverter arrangement, such that the control signaloutput 476 will be the logical opposite of switch signal input 462.However, any suitable switching means may be used to switch thetransistors 466 and 468. The circuit schematic of FIG. 4C differs fromthe schematic of FIG. 4B by depicting current source 470 and currentsource 472 as being between PMOS transistor 466 and NMOS transistor 468.It should be understood that charge pump 461 may be implemented using avariety of circuit arrangements that are capable of controlling the rateof rise and fall of the control signal outputs (e.g. 476) such that thechanges are slow enough to substantially reduce or eliminate glitcherrors but rapid enough to provide a sufficiently high amplifier slewrate.

FIG. 4D illustrates an exemplary operating sequence for TGC controlsignals, according to a non-limiting embodiment of the presentapplication. FIG. 4D shows the time variation of three control signalswitching signals, SW0 signal 480, SW1 signal 482, and SW2 signal 484.The switching signals 480, 482, 484 may be generated by amicrocontroller, timing circuitry, a processor, or any other suitablecontrol circuitry. In some implementations, one or more (e.g., each) ofthe switching signals has a respective, corresponding control signal.For example, the SW0 signal may correspond to the CTRL[0] signaldiscussed with reference to FIGS. 4A and 4B, the SW1 signal maycorrespond the CTRL[1] signal, and the SW2 signal may correspond to aCTRL[2] signal or the CTRL[N] signal. Initially, the SW0 signal 480 is alogical zero (a low signal that may be equivalent to ground), while theother signals are logical ones (high signals that may be equivalent tothe supply voltage). When output to the TGC control signal switchingcircuit 460 discussed with reference to FIG. 4B, a logically low SW0switch signal will cause the corresponding CTRL[0] control signal to beasserted as logically one, which in turn opens a feedback path asdiscussed with reference to FIG. 4A. In this example, having only theSW0 signal 480 logically zero creates a single resistor feedback pathand activates the lowest gain setting in the amplifier 112. At time T1,the SW0 signal 480 is switched to a logical one, e.g., as discussed withreference to FIG. 4B, and the SW1 signal 482 is switched to a logicalzero, while the SW2 signal 484 remains logically one. This increases theresistance of the exemplary variable impedance feedback circuit 334 asdiscussed with reference to FIG. 4A and, thereby, increases the gain ofthe amplifier 112. At a time T2 that is later than time T1, the SW0signal 480 remains logically one, the SW1 signal 482 is switched fromlogical zero to logical one, and the SW2 signal 484 is switched fromlogical one to logical zero, thereby further increasing the impedance ofvariable impedance feedback circuit 334 and further increasing the gainof the amplifier 112. This sequence of temporally, sequentiallyincreasing gain provides TGC functionality to the amplifier 112.

It should be appreciated that the sequence illustrated in FIG. 4D isnon-limiting. For example, the number of time periods and switchingsignals shown are not limiting. In some implementations, multipleswitching signals and corresponding control signals may be asserted highor low at a given time, e.g., to permit for different arrangements ofswitching and variable impedance circuitry or to allow for more finegrained control of the impedance and gain than is allowed by a seriesarrangement of resistors.

Having thus described several aspects and embodiments of the technologyof this application, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those of ordinaryskill in the art. Such alterations, modifications, and improvements areintended to be within the spirit and scope of the technology describedin the application. It is, therefore, to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto,inventive embodiments may be practiced otherwise than as specificallydescribed. For example, while several embodiments have been described asemploying a TIA, other amplifiers may alternatively be used, includingLNAs and trans-conductance amplifiers. More generally, voltageamplifiers may be implemented, and may be beneficial when the ultrasounddevice includes a transducer which outputs a voltage signal, such as apiezoelectric crystal transducer. Other variations are possible.

As described, some aspects may be embodied as one or more methods. Theacts performed as part of the method(s) may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements.

As used herein, the term “between” used in a numerical context is to beinclusive unless indicated otherwise. For example, “between A and B”includes A and B unless indicated otherwise.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively.

1. An ultrasound apparatus, comprising: an ultrasonic transducer toprovide an analog electrical signal; an amplifier having time gaincompensation (TGC) functionality coupled to the ultrasonic transducerand configured to receive and amplify the analog electrical signal by atime-dependent amount.
 2. The ultrasound apparatus of claim 1, whereinthe time-dependent control signal from the charge pump is configured tocontrol, at least in part, the impedance of the feedback circuitry ofthe amplifier such that the impedance of the feedback circuitry varieswith time.
 3. The ultrasound apparatus of claim 1, wherein the chargepump is configured to receive as an input signal a switching signal thatis either a logical zero or a logical one.
 4. The ultrasound apparatusof claim 3, wherein the charge pump is configured to receive theswitching signal from a microcontroller, timing circuitry, or aprocessor.
 5. The ultrasound apparatus of claim 3, wherein the chargepump is configured to slow edges of the time-dependent control signalduring transitions between logic levels of the switching signal.
 6. Theultrasound apparatus of claim 5, wherein the charge pump is configuredto output the time-dependent control signal with a maximum transitiontime of 0.005 dB per 10 nanoseconds, 0.01 dB per nanosecond, 0.1 dB pernanosecond, or 0.2 dB per nanosecond.
 7. The ultrasound apparatus ofclaim 3, wherein the switching signal is a first switching signal, andwherein the charge pump is configured to receive as input signalsmultiple switching signals, including the first switching signal,asserted low or high in a time-varying manner.
 8. The ultrasoundapparatus of claim 1, wherein: the feedback circuitry comprises atransistor having a gate; and the time-dependent control signal from thecharge pump is electrically coupled to the gate of the transistor in thefeedback circuitry.
 9. The ultrasound apparatus of claim 8, wherein: thefeedback circuitry further comprises a resistor; and the transistor inthe feedback circuitry is electrically coupled to the resistor in thefeedback circuitry and configured to switch the resistor into or out ofa feedback path of the feedback circuitry.
 10. The ultrasound apparatusof claim 1, wherein the charge pump comprises: an inverter having aninput node and an output node; and a capacitor coupled to the outputnode of the inverter; wherein: the charge pump is configured to outputthe time-dependent control signal on the output node; and the chargepump is configured to receive a switching signal on the input node as aninput signal.
 11. A method of operating an ultrasound apparatus havingan ultrasonic transducer, an amplifier coupled to the ultrasonictransducer and comprising feedback circuitry having an impedance, and acharge pump coupled to the feedback circuitry, the method comprising:operating the charge pump to output to the amplifier a time-dependentcontrol signal configured to control, at least in part, the impedance ofthe feedback circuitry of the amplifier.
 12. The method of claim 11,wherein operating the charge pump to output to the amplifier thetime-dependent control signal comprises operating the charge pump tooutput to the amplifier a time-dependent control signal configured tovary the impedance of the feedback circuitry of the amplifier with time.13. The method of claim 11, wherein operating the charge pump comprisesoperating the charge pump to receive as an input signal a switchingsignal that is either a logical zero or a logical one.
 14. The method ofclaim 13, wherein operating the charge pump to receive the switchingsignal comprises operating the charge pump to receive the switchingsignal from a microcontroller, timing circuitry, or a processor.
 15. Themethod of claim 13, wherein operating the charge pump comprisesoperating the charge pump to slow edges of the time-dependent controlsignal during transitions between logic levels of the switching signal.16. The method of claim 15, wherein operating the charge pump to outputthe time-dependent control signal comprises outputting thetime-dependent control signal with a maximum transition time of 0.005 dBper 10 nanoseconds, 0.01 dB per nanosecond, 0.1 dB per nanosecond, or0.2 dB per nanosecond.
 17. The method of claim 13, wherein the switchingsignal is a first switching signal, and wherein operating the chargepump comprises operating the charge pump to receive as input signalsmultiple switching signals, including the first switching signal, andwherein the method further comprises asserting the multiple switchingsignals low or high in a time-varying manner.
 18. The method of claim11, wherein the feedback circuitry comprises a transistor having a gate,and wherein operating the charge pump to output the time-dependentcontrol signal comprises operating the charge pump to output thetime-dependent control signal to the gate of the transistor in thefeedback circuitry.
 19. The method of claim 18, wherein the feedbackcircuitry further comprises a resistor electrically coupled to thetransistor in the feedback circuitry, and wherein operating the chargepump to output the time-dependent control signal to the gate of thetransistor comprises switching the resistor into or out of a feedbackpath of the feedback circuitry.
 20. The method of claim 11, wherein thecharge pump comprises an inverter having an input node and an outputnode, and a capacitor coupled to the output node of the inverter,wherein: operating the charge pump to output the time-dependent controlsignal comprises operating the charge pump to output the time-dependentcontrol signal on the output node of the inverter; and the methodfurther comprises receiving a switching signal on the input node of theinverter.